Four years and 217 days after he rode a camel into his 30th birthday party, Adrian Peterson now wears the workhorse saddle upon which Redskins interim coach Bill Callahan will ride into U.S. Bank Stadium for Thursday night’s game against Peterson’s former team.

So, Bill, you old-school O-line coach, exactly how much football do you think is left in Peterson, who, by the way, said Tuesday he is “for sure” playing Thursday on his nicked-up ankle.

“Oh my gosh,” Callahan said Tuesday. “He’s got so much in him.”

Actually, Callahan answered that question two days earlier, not with words but rather a scripted play sheet to open the windy, rain-soaked 9-0 home loss to San Francisco.

Peterson off right tackle for 14 yards … Peterson left end for 5 yards … Peterson left guard for 3 yards … Peterson left tackle for 2 yards … Peterson right tackle for 4 yards … Peterson right end for 4 yards … Peterson right guard for 3 yards …

That’s right. Seven plays, seven Peterson runs. He had another carry in the 10-play drive that ended with a missed 39-yard field-goal attempt.

“He’s just rare,” said Callahan, who is 1-1 since replacing the fired Jay Gruden after an 0-5 start. “His offseason training regimen is really unique. … I think he’s one player that certainly takes advantage of every resource that he can.”

Chiseled Vikings defensive end Danielle Hunter sees that firsthand four to five times a week every offseason. He and other Houston-based NFL players work out alongside Peterson while swearing by grueling taskmaster James Cooper, Peterson’s longtime trainer and co-owner of the O Athletik, the gym Peterson opened in 2016.

“The harder it gets, the more and more determined Adrian gets to get that next rep, finish another lap,” Hunter said. “He just gets that look. How he takes care of his body is something I admire, and it’s where I get some of the way I take care of my body.”

Give us a good example, Danielle.

“We’ll do legs with maybe 10 sets of squatting with heavy weights,” he said. “We’ll darn near almost die. But then we go run the track. Or runs miles in the sand pit, changing directions. Or run up a steep hill 20 times. Or bear crawl up the hill backward.

“You come out of the squats and your legs feel like Jell-O. You’re thinking, ‘How in the world am I going to be able to go run?’ Then you push yourself. Everything we do is about muscle endurance.”

The old-timers club

Hunter was a 20-year-old rookie in 2015 when a 30-year-old Peterson won his third NFL rushing title with 1,485 yards on a league-high 327 carries. Peterson also joined Marion Motley and Curtis Martin as the only players to win a rushing title in their 30s. Motley was 30 in 1950 and Martin was 31 in 2004.

Fast forward four years and, according to Callahan, “He’s looking like the same old Adrian that we all know.” Or, as Vikings coach Mike Zimmer put it, “Typically, [power runners], once they get older, they slow down. He’s always had the speed and the physicality of the way he runs. Typically, those guys get beat up once they get older, and I don’t see that with him.”

After rushing for a combined 601 yards with the Vikings, Saints and Cardinals in 2016-17, Peterson joined the Redskins last year and became the fifth player in NFL history to reach 1,000 yards rushing (1,042) after age 32. The others: Frank Gore (2016), John Riggins (1983 and 1984), Franco Harris (1983) and John Henry Johnson (1964).

Riggins is the oldest player to reach 1,000 yards, doing it at 35 years and 106 days in 1984. Johnson did it at 35 years and 12 days in 1964.

“How long can Adrian play?” Hunter asked. “He’s a strong dude. He doesn’t look 34. The way he moves, sometimes you just wonder, ‘How in the world can somebody that age who’s played [13 seasons] move the way he moves. He’s doing a whole bunch of stuff he shouldn’t be doing.”

Peterson is under contract through 2020. In modern NFL history, Marcus Allen is the benchmark for running back longevity. He was 37 years and 284 days when he played his final game on Jan. 4, 1998. For all of NFL history, the Pro Football Hall of Fame lists Jim Thorpe as playing halfback at age 40 in 1928.

Thorpe played only one game that season. And it was only for a few minutes of the Chicago Cardinals’ 34-0 Thanksgiving Day loss to the Bears at Wrigley Field. And, by the way, if you still have your $2 ticket stub from that game, it’s worth a tad more than two bucks.

Heading to 1,000?

Assuming he stays healthy, Peterson’s career has been reborn under Callahan for the remainder of this season. And it comes a month after Gruden made Peterson a healthy scratch on opening day and then explained his decision by saying, “If we have a game where we think we can run the ball 55 times from an I-formation, then sure, I’ll get him up.”

In five games under Gruden this year, Peterson had 43 touches (40 carries). In two games under Callahan, he’s had 45 touches (43 carries). He had 23 carries for 118 yards (5.1 yards per carry) in the 17-16 win at Miami and 20 carries for 81 yards (4.1) but also lost a fumble and was stopped for no gain on fourth-and-1 against the 49ers.

If Peterson gets 20 carries Thursday night, it would be the first time since 2015 that he’s had at least that many in three straight games. With 307 yards rushing, he needs to average 77 a game for his ninth 1,000-yard season. He’s averaging 99.5 under Callahan.

Tuesday, Peterson was asked by Washington reporters if there’s more motivation facing the Vikings.

“Of course,” he said before likening his feeling to those of quarterbacks Case Keenum and Kirk Cousins, who were on opposite sides back in 2017.

“We’re all human. I’m sure Case wants to stick it to them just like I want to stick it to them. And just like Kirk Cousins wants to stick it to us. It’s all mutual feelings.”

The Vikings, of course, have a new running back they believe is the best in football. His name is Dalvin Cook. He’s 10 years younger, has more versatility and leads the league in rushing.

Just beware when underestimating Peterson.

“He’s still explosive, has good change of direction, good vision and is still breaking tackles and outrunning people,” Hunter said. “To this day, I’m still like, ‘Man, this dude still has it after all these years.’”